It is known to employ nickel base superalloys in the fabrication of aircraft engine components. To be acceptable, such alloys must exhibit good castability with no heat treat cracking, good high temperature longitudinal and transverse creep strength properties and good hot corrosion resistance.
One such nickel base superalloy employed as a turbine blading material in aircraft engines is single crystal (SC) Rene N4 alloy. A form of SC Rene N4 is described in U.S. Pat. No. 5,154,884 as a nickel-base superalloy composition comprising, by weight, 7-12% Cr, 1-5% Mo, 3-5% Ti, 3-5% Al, 5-15% Co, 3-12% W, up to 10% Re, 2-6% Ta, up to 2% Cb, up to 3% V, up to 2% Hf, the balance being essentially nickel and incidental impurities. U.S. Pat. No. 5,399,313 describes a modified version of SC Rene N4 as comprising, by weight, 9.5-10.0 Cr, 7.0-8.0 Co, 1.3-1.7 Mo, 5.75-6.25 W, 4.6-5.0 Ta, 3.4-3.6 Ti, 4.1-4.3 Al 0.4-0.6 Cb, 0.1-0.2 Hf, 0.05-0.07 C and 0.003-0.005 B, the balance being nickel and incidental impurities.
Typically, aircraft engine blades are small, on the order of a few inches long, and weigh a few ounces, or a few pounds at most. Power turbine buckets, by contrast, are typically up to about 36 inches long, and weigh up to about 40 pounds. It has been found that use of single crystal alloys for such large parts is impractical. A need exists for a superalloy for use in the fabrication of large turbine blades which exhibits good castability with no heat treat cracking, good high temperature longitudinal and transverse creep strength properties and good hot corrosion resistance. The present invention seeks to satisfy that need.